It is proposed to subject 3,200 families to a 3-hour testing session in which a battery of 16 psychometric tests, measuring various cognitive abilities, and an environmental questionnaire are completed by father, mother and at least one child over 14 years of age, a blood and saliva sample is taken for blood groups and genetic marker studies, and finger and palm prints are collected. So far 1051 families have been tested, mainly of Caucasian and Japanese ancestry. The objectives of the study are (1) to estimate the heritabilities and genetic correlations of scores on the selected cognitive tests, (2) to compare phenotypic and genetic cognitive factor structure, (3) to measure the effects of inbreeding, assortative mating, ancestry, parental age, birth order, certain maternal-fetal risks, and socio- economic variables, (4) to search for possible relationships between cognitive traits and genetic markers, and between cognitive and dermatoglyphic traits, and (5) to search for non-additive genetic effects (heterosis, dominance, epistasis) in components of the cognitive abilities tested.